e chronological data which have come down to us for this period
are too scanty to allow of any exact statement of the number of years
occupied by Mithridates in effecting these conquests. All that can be
said is that he appears to have commenced them about B.C. 163 and to
have concluded them some time before B.C. 140, when he was in his turn
attacked by the Syrians. Probably they had been all effected by the
year B.C. 150; since there is reason to believe that about that time
Mithridates found his power sufficiently established in the west to
allow of his once more turning his attention eastward, and renewing his
aggressions upon the Bactrian kingdom, which had passed from the rule of
Eucratidas under that of his son and successor, Heliocles.

Heliocles, who was allowed by his father a quasi-royal position,
obtained the full possession of the Bactrian throne by the crime of
parricide. It is conjectured that he regarded with disapproval his
father's tame submission to Parthian ascendency, and desired the
recovery of the provinces which Eucratidas had been content to cede for
the sake of peace. We are told that he justified his crime on the ground
that his father was a public enemy; which is best explained by supposing
that he considered him the friend of Bactria's great enemy, Parthia.
If this be the true account of the circumstances under which he became
king, his accession would have been a species of challenge to
the Parthian monarch, whose ally he had assassinated. Mithridates
accordingly marched against him with all speed, and, easily defeating
his troops, took possession of the greater part of his dominion. Elated
by this success, he is said to have pressed eastward, to have invaded
India, and overrun the country as far as the river Hydaspes, but, if
it be true that his arms penetrated so far, it is, at any rate, certain
that he did not here effect any conquest. Greek monarchs of the Bactrian
series continued masters of Oabul and Western India till about B.C. 126;
no Parthian coins are found in this region; nor do the best authorities
claim for Mithridates any dominion beyond the mountains which enclose on
the west the valley of the Indus.

By his war with Heliocles the empire of Mithridates reached its greatest
extension. It comprised now, besides Parthia Proper, Bactria, Aria,
Drangiana, Arachosia, Margiana, Hyrcania, the country of the Mardi,
Media Magna, Susiana, Persia and Babylonia. Very probably its limits